Verizon plans to increase ARPU with tiered pricing (here), will become a reality soon, based on volume based billing and tethering surcharge. The speed factor mentioned before is not there - probably waiting for broader LTE coverage and availability of devices.
Droid life reports that "we’ve just received word that tiers are scheduled to start the day after the promo ends (on the 7th) for new customers and will look something like this… Data plans: 2GB – $30/month; 5GB – $50/month; 10GB – $80/month. If you would like to add tethering on to any of those packages, you can purchase 2GB of data at an additional cost of $20 per month"
See "Exclusive: Tiered Data Plans Headed to Verizon July 7, Packages Start at $30 for 2GB" - here.
Detection of tethering requires some network intelligence - see how AT&T does it (here). See also "Openet CMO:"Verizon prepared their network with a policy management infrastructure sufficiently in place, to handle the volume increase with stride" - here.
The site got a letter sent to Verizon employees (here) by one of Verizon's Area VP of Marketing and Sales Operations, saying: "..Our legacy data pricing structure was designed to address a somewhat different customer need profile than what we are seeing and can expect in the future .. Data usage has more than doubled over the last three years. .. Whether it’s social media (85%+ of Smartphone users), mobile internet (88%+ of Smartphone users), or email/applications (71%+ of Smartphone users), this usage has one thing in common—dramatically increased demand for data and media consumption... As a result, we are evolving our approach around how we package our data solutions and pricing to our customers. Coming soon, Verizon Wireless will move from our existing pricing format to a structure designed to allow customers to choose the right data solution that best aligns with their needs .. The successful launch of our new data pricing solutions represents a key milestone in our continued march to excellence".